1. Field of the Invention
The present invention relates to a liquid crystal display, and particularly relates to a liquid crystal display in which the birefringence function of liquid crystal molecules is controlled by a voltage.
2. Description of the Related Art
FIGS. 2A and 2B show an example of a homeotropic liquid crystal display according to a conventional technique.
FIG. 2A shows a schematic configuration of a cell of the hometropic liquid crystal display. Two sets of transparent electrodes 22 and 24 are formed on the opposite surfaces of a pair of glass substrates 21 and 25, respectively. The sets of electrodes 22 and 24 are elongated in the y and x directions respectively. Liquid crystal molecules 23 are sandwiched between the pair of glass substrates 21 and 25 so as to constitute a liquid crystal cell 20. When no electric field is applied to the liquid crystal molecules 23, the liquid crystal molecules 23 show a homeotropic orientation substantially perpendicular to the respective surfaces of the substrates 21 and 25. Each liquid crystal molecule 23 has an elongated shape, and has a high refractive index in its axial direction. In addition, each liquid crystal molecule 23 has an electric dipole in a direction perpendicular to its axial direction. Upon application of a voltage across the two sets of electrodes 22 and 24, each liquid crystal molecule 23 is tilted toward the direction parallel to the respective surfaces of the substrates 21 and 25 by the action of an electric field. In order to control the direction of this tilt, the respective surfaces of the substrates 21 and 25 and the electrodes 22 and 24 are subjected to orientation treatment in advance. The orientation treatment is performed so as to orientate liquid crystal molecules along the y direction. Therefore, when no electric field is applied, each liquid crystal molecule has a pretilt which is directed to the y direction slightly. When an electric field is applied, the liquid crystal molecule tilts so as to fall along the y direction.
A pair of crossed polarizers 10 and 30 are disposed outside the substrates 21 and 25 respectively. Polarization axes P1 and P2 of these polarizers 10 and 30 are disposed at an angle of 45.degree. relative to the x and y axes respectively as shown in FIG. 2B.
If the liquid crystal molecules are aligned along the y direction by the action of an electric field, light transmitted through the polarizer 10 is depolarized by the liquid crystal layer by the birefringence of the liquid crystal molecules so that the light can transmit through the other polarizer 30.
When the liquid crystal molecules are in homeotropical orientation, the birefringence of the liquid crystal molecules have no effect on the transmitted light, so that the light transmitted through the one polarizer reaches to the other polarizer as it is while keeping its polarization state, and the light is cut off by the action of the crossed polarizer to show a dark state.
As to the details of such a homeotropic liquid crystal display, for example, reference is made to "Homeotropic-Alignment Full-Color LCD", SID, '89.